Assessment Comments
Assessment is based on results of an IDNR investigation of a fish kill in August 2005.
Basis for Assessment
SUMMARY: The general uses of this stream are assessed (monitored) as “partially supported” due to a fish kill in August 2005. Although the cause of this kill was not identified, a pollutant cause is suspected. The party responsible for the kill was not identified. This impairment is appropriate for Category 5b of Iowa’s 2006 Integrated Report (=Section 303(d) list).
EXPLANATION: This kill occurred on or before August 12, 2005. The kill occurred in the SE ¼ of Section 35, T88N, R2W, Dubuque Co.; approximately 0.25 miles of stream was affected. Despite a thorough investigation of the kill by IDNR field staff, no cause or source of the kill was identified. Although no estimate was given for the number of fish killed, comments from the investigation note that “suckers, chubs and minnows” were killed. Investigators concluded that this localized kill may have been caused by combination of factors; for example, manure plus lignin sulfonate (recently sprayed on a nearby road for dust control) in combination with a rainfall event of approximately 1 inch on the night of August 11. This is the first kill reported for this segment of Johns Creek. A kill occurred in the lower reach of Johns Creek (IA 01-NMQ-0110-0) in July 1985.
According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2002-2005) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill is identified, and the cause is either known, or suspected, to be a “pollutant”, the assessment type is considered “monitored” and the affected waterbody is a candidate for Section 303(d) listing. Fish kills attributed to a pollutant, but where a source of the pollutant was not identified, will be placed into Integrated Report subcategory 5b. The intent of placing these waterbodies into Category 5 is not to necessarily require a TMDL but to keep the impairment highlighted due to the potential for similar future kills from the unaddressed causes and/or sources.
